In the last video, we saw the
classification of elements into groups on the
periodic table, and we stopped
with the definition for a transition metal. There are two ways to think
about transition metals. So one way to think about it
would be when some teachers say transition metal,
they're talking about elements found from
Groups 3 through Group 12. So all the elements
in here, some people consider these to be
the transition metals. So these are the elements
found in the d block, right? So we're talking
about d orbitals here. So you have to understand
electron configurations for this video. So that's one way to think
about the transition metals, but that way is maybe a little
bit too general sometimes. So there is another
definition, which you'll find in
the IUPAC website. IUPAC is an acronym for
International Union of Pure and Applied Chemistry, and they
say that a transition element refers to an element whose atom
has an incomplete d subshell. So when you're talking
about the d orbitals, we already know there
are five d orbitals, and each orbital holds a
maximum of two electrons. So 5 times 2 is 10. So 10 will be the maximum
number of electrons that you could fit in your d
orbitals, or your d subshells. So let's count that out on our
periodic table so 10, so 1, 2, 3, 4, 5, 6, 7, 8, 9,
10 for our d block. So let's go ahead and write
an electron configuration for a transition
metal and let's see how that applies to our
definition from IUPAC. So let's write an electron
configuration for iron. So here's iron right here. And if I wanted to write
an electron configuration, let's say I wanted to
do noble gas notation. So once again, I'm assuming that
you know how to do this already so I won't spend too much
time talking about it. But if I want to write a
noble gas configuration, I would go to argon, which
is the noble gas before iron, and I would put argon
in brackets like that. And that takes me to
the fourth energy level or the fourth period
on the periodic table. And then just looking
at the periodic table, I can say, oh, that
would be 4s1, 4s2, so I can write 4s2 here. And then I'm in my d orbitals. So, again, just looking
at the periodic table to write my electron
configuration, I would say 1, 2, 3,
4, 5, 6 electrons. So that would be 3d6. And I could have
written this 3d6 4s2. And right now,
both are considered to be correct answers. And I won't get
into a discussion about the order of filling of
these orbitals in this videos. So I'll save that
for another video. This video is only
talking about definitions and identifying elements
on the periodic table. And so either one of these
would be a correct electron configuration. And when I look at the d
orbitals for the electron configuration, I
can see that there are six electrons
in my d orbitals. Well, that's an
incomplete d subshell, because I can fit a total
of 10 into my d orbitals. And so iron would be an example
of an element whose atom has an incomplete d subshell. So iron is a transition metal. Let's write the electron
configuration for zinc. So let's find zinc over
here, so right there on pour periodic table. So if I wanted to write
the electron configuration for zinc, once again, I
would go to the noble gas before it, which is argon. So I would put in
brackets argon right here. And then, once again, it takes
me to the fourth energy level. So 4s1, 4s2, so 4s2. And then I count over for my d
electrons-- 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. So it would be 3d10. And once again, I
could have written that argon in brackets 3d10 4s2. So it doesn't matter. So let's think
about the definition for a transition
metal, an element whose atom has an
incomplete d subshell. Well, if I look at the
d orbitals for zinc, they are completely full. I have 10 electrons
in my d orbital, and so this is a
complete d subshell. So this does not
meet the definition for a transition element. Now, also in the definition,
it talks about cations. So let's think about to the
cation that zinc would form. Zinc would go to zinc 2 plus. So if I wanted to write the
electron configuration for zinc 2 plus, I need to think
about where does zinc lose two electrons? So if you've going from
a neutral atom of zinc to zinc 2 plus, you would
have to lose two electrons. Well, I already know
that those two electrons are going to be lost
from the 4s orbitals. So we're going to lose these
two electrons right here on your electron configuration,
and so you'd be left with 3d10. And once again,
you have a cation that has a complete d subshell. You've completely
filled your d orbitals, and so the cation does not have
an incomplete d subshell, which means that it doesn't fit
our technical definition for a transition
element from IUPAC. And so, once again, there are
two ways of thinking about it. One's a very general way. So you might hear someone talk
about an element from Groups 3 through to 12 as being
a transition metal, or you might find people
who are a little bit more particular about the definition,
who go along with IUPAC. It's good to be aware of both
ways of thinking about it.